Interview Questions.

Question 1. What Is Sip?

Answer :

The Session Initiation Protocol (SIP) is a signaling, presence and immediate messaging protocol developed to set up, alter, and tear down multimedia periods, request and deliver presence and immediately messages over the Internet. SIP is a text-encoded protocol.

Question 2. What Is Request-uri?

Answer :

The Request-URI is a special form of SIP URI and indicates the useful resource to which the request is being despatched, additionally referred to as the request target.

Voice Over Internet Protocol (VOIP) Interview Questions
Question 3. What Is The Significance Of The Via Header Field?

Answer :

Each SIP device that originates or forwards a SIP message stamps its personal cope with in a "Via" header subject, normally written as a number call that can be resolved into an IP address the use of a DNS query. The Via header field carries the SIP version number (2.Zero), a “/”, then UDP for UDP shipping, a area, then the hostname or address, a colon, then a port quantity. And additionally include "branch" parameter.

Question 4. Where The Branch Parameter Is Used And What Is Its Significance?

Answer :

A "department" parameter is used in "Via" header subject. It is signified because the transaction identifier used to correlate the reponses to the request.

Internet Protocol model 6 (IPv6) Tutorial
Question 5. What Is The Significance Of Max-forwards Header Field?

Answer :

Max-Forwards header field is used for easy loop detection. It is initialized to a few massive integer and decremented by each SIP server which receives and forwards the request.

Veritas Volume Manager (VVM or VxVM) Interview Questions
Question 6. What Are The Significance Of To And From Header Fields?

Answer :

To and From header fields show the originator and vacation spot of the SIP request.

Question 7. Why The Name Labels Will Be Used In To And From Header Fields?

Answer :

When a name label is used, the SIP URI is enclosed in brackets and used for routing the request.The call label will be displayed at some point of alerting, however is not used by the protocol.

Internet Protocol version four (IPv4) Tutorial Simple Mail Transfer Protocol (SMTP) Interview Questions
Question 8. What Is The Sigificance Of The Call-identity Header Field?

Answer :

The Call-ID header field is an identifier used to preserve song of a selected SIP consultation. The originator of the request creates a locally unique string, then normally adds an “@” and its host call to make it globally specific. In addition to the Call-ID, every party inside the consultation additionally contributes a random identifier, specific for every call. These identifiers, called tags, are blanketed inside the To and From header fields as the session is established. The consumer agent that generates the initial INVITE to set up the consultation generates the particular Call-ID and From tag. In the reaction to the INVITE, the user agent answering the request will generate the To tag. The aggregate of the neighborhood tag (contained inside the From header subject), remote tag (contained within the To header field), and the Call-ID uniquely identifies the installed consultation, called a “dialog.” This conversation identifier is utilized by both events to discover this name due to the fact they might have a couple of calls installation among them. Subsequent requests inside the set up session will use this dialog identifier.

Question 9. What Is Dialog Identifier?

Answer :

The combination of the local tag (contained inside the From header area), remote tag (contained in the To header field), and the Call-ID uniquely identifies the set up consultation, known as a “dialog.” This dialog identifier is used by both parties to become aware of this call because they could have more than one calls set up among them. Subsequent requests in the established session will use this dialog identifier.

Internet Protocol model 6 (IPv6) Interview Questions
Question 10. When The Cseq Header Field Value Will Be Incremented? Or What Is The Significance Of Cseq Header Field?

Answer :

CSeq or Command Sequence includes various followed with the aid of method call.This range is incremented for every new request despatched.

Question eleven. What Are The Minimum Required Header Fields In Any Sip Message?

Answer :

Via, Max-Forwards, To, From, Call-ID and CSeq are the minimal required header fields.

Internet Protocol model four (IPv4) Interview Questions
Question 12. What Is The Significance Of Contact Header Field?

Answer :

Contact header subject contains the tool-URI wherein the originator of request or reaction can be at once reached. Usually consists of IP deal with of the device which generated the request or reaction.

Voice Over Internet Protocol (VOIP) Interview Questions
Question thirteen. What Is Received Parameter And In Which Header Field It Will Be Appeared?

Answer :

Usually the received parameter may be observed in Via header field of the response message. This parameter contains the literal IP cope with that the request was acquired from, which typically is the equal address that the URI in the Via resolves using DNS.

Question 14. Is The To And From Header Fields Define The Direction Of The Sip Message?

Answer :

No, the To and From header fields in SIP are defined to signify the course of the request, not the path of the message.

Question 15. Is The Branch Parameter In Via Header Field Of The Ack Sent For 200ok Would Be Same As That Of Invite In A Session?

Answer :

No, branch parameter in Via header area of the ACK would be exclusive than the INVITE message of that consultation due to the fact ACK sent to renowned the 200OK is taken into consideration as a seperate transaction.

Spanning Tree Protocol (STP) Interview Questions
Question 16. Is The Branch Parameter In Via Header Field Of The Bye Message Would Be Same As Ack Sent For 200ok And That Of Invite In A Session?

Answer :

No, because BYE message is considered as a brand new transaction.

Question 17. What Is Dialog?

Answer :

A conversation is a peer-to-peer SIP courting between two UAs that persists for a while.  A conversation is set up by SIP messages, together with a 2xx response to an INVITE request.  A dialog is identified by using a name identifier, local tag, and a faraway tag.  A conversation become formerly called a name leg in RFC2543.

Border Gateway Protocol (BGP) Interview Questions
Question 18. What Is A Session?

Answer :

A multimedia session is a set of multimedia senders and receivers and the facts streams flowing from senders to receivers. A multimedia conference is an instance of a multimedia consultation.

Veritas Volume Manager (VVM or VxVM) Interview Questions
Question 19. What Is The Difference Between Dialog And Session?

Answer :

A dialog is a sip courting. A session is a media courting. Dialog imply a "call has already been setup" in the signaling sense, at the same time as a session mean the "media has already been setup" in the media feel.

Question 20. What Does "component Of A Dialog" Mean? Are "invite", "ack" And The Responses Considered "element Of A Dialog"?

Answer :

Dialog represents kingdom, which incorporates series numbers, path sets, and URIs. A request sent as a part of a conversation means that it includes direction headers from the direction set of the dialog, and uses the next highest series quantity in the dialog.

Enhanced Interior Gateway Routing Protocol (EIGRP) Interview Questions
Question 21. What Does "out of doors The Dialog" Mean Then? Is A Request Is Outside The Dialog, Does It Still Affect Or Change Anything "interior The Dialog" Then?

Answer :

Outside the dialog means that it isn't inside the context of a dialog. It doesnt use the callid, cseq, or course sets of any present dialogs, and while such a reuqest is set, it has no impact on the nation of an present dialog.

Question 22. What Is The Advantage Of Using Sip Uris? Over Ip Address?

Answer :

A request routed the usage of best IP addresses will reach only one give up point—most effective one device. Since verbal exchange is commonly user-to-user in place of tool-to-tool, a extra beneficial addressing scheme might allow a specific consumer to call every other specific consumer, which would result in the request accomplishing the goal person no matter which he is presently the use of, or if he has multiple devices.SIP URI is a name this is resolved to an IP deal with through the usage of SIP proxy server and DNS lookups at the time of the call.

Question 23. What Is Sip Uri?

Answer :

SIP URI is a call this is resolved to an IP address with the aid of the use of SIP proxy server and DNS lookups on the time of the decision.

Post Office Protocol (POP) Interview Questions
Question 24. What Is Sip Proxy Server?

Answer :

A SIP proxy server sits within the middle of SIP message alternate, receives messages and forwards them, but it does not set up or terminate periods. A proxy server usually has get right of entry to to a database or a place carrier to resource it in processing the request (determining the subsequent hop). Databases should include SIP registrations, presence information, or any other form of information about where a user is positioned.

Simple Mail Transfer Protocol (SMTP) Interview Questions
Question 25. What Is Stateful Proxy?

Answer :

A stateful proxy server continues tune of requests and responses acquired within the beyond and uses that facts in processing destiny requests and responses. For instance, a stateful proxy server begins a timer while a request is forwarded. If no reaction to the request is obtained within the timer duration, the proxy will retransmit the request, relieving the user agent of this assignment. A stateful proxy usually sends a one hundred Trying response whilst it gets an INVITE.

Question 26. What Is Stateless Proxy?

Answer :

A stateless proxy server techniques each SIP request or reaction most effective based totally at the message contents. Once the message has been parsed, processed, and forwarded or spoke back to, no records about the message is stored—no dialog statistics is saved. A stateless proxy in no way retransmits a message, and does no longer use any SIP timers.A stateless proxy never sends a one hundred Trying reaction.

Question 27. What Is Transaction Stateful Proxy?

Answer :

A transaction stateful proxy continues state about a transaction but most effective for the length that the request is pending. For example, a transaction stateful proxy would maintain state while it receives an INVITE request till it received a 2 hundred OK or a very last failure reaction (e.G., 404 Not Found). After that, it would destroy the country information. This lets in a proxy to carry out useful seek offerings but limit the amount of nation storage required.

Internet Protocol model 6 (IPv6) Interview Questions
Question 28. How The Proxy Server Is Different From A User Agent Or Gateway?

Answer :

A proxy server isn't the same as a gateway or person agent in 3 key methods:

A proxy does not problem request, it most effective responds to requests from person marketers. (A CANCEL request is an exception to this rule)
A proxy server has no media competencies.
A proxy server does now not parse message bodies, it relies completely on message header fields.
Question 29. What Is Outbound Proxy Server?

Answer :

The proxy server to which the person agent sends the SIP request is known as the outbound proxy server. This proxy server will authenticate the consumer agent and can pull up a profile of the user and practice outbound routing services.

Question 30. What Is Inbound Proxy Server?

Answer :

The proxy server from which the user agent recieves the SIP request is known as the inbound proxy server.

Question 31. What Is Forking Proxy Server?

Answer :

a proxy server that gets an INVITE request, then forwards it to a number of places at the equal time. This “forking” proxy server keeps music of every of the super requests and the reaction to every. This is useful if the area carrier or database lookup returns more than one viable places for the referred to as birthday celebration that need to be tried. For instance forking proxy F1 is received from UA1 which forks to 2 person dealers UA2 & UA3. Each consumer agent starts alerting and sending returned  provisional resposes(180 Ringing) to F1. The two responses are equal except for having one-of-a-kind To tags and Contact URIs. Finally, one of the  UAs solutions and sends a 2 hundred OK reaction. The forking proxy server sends a CANCEL to the second one UA to stop that telephone alerting. If each UAs had replied, the forking proxy might have forwarded each two hundred OK responses again to the caller who then would have needed to pick out which one, possibly accepting one and sending a BYE to the other one.

Question 32. Explain About Session-expires Header Field?

Answer :

A SIP session timer has been proposed to limit the time period over which a stateful proxy should preserve country statistics. In the preliminary INVITE request, a Session-Expires header subject indicates a timer c programming language and then stateful proxies may additionally discard country data approximately the consultation. User marketers need to tear down the call after the expiration of the timer. The caller can ship re-INVITEs to refresh the timer, allowing a “hold alive” mechanism for SIP. This solves the hassle of the way long to shop nation facts in instances wherein a BYE request is misplaced or misdirected.

Question 33. What Is Redirect Server?

Answer :

A redirect server is a form of SIP server that responds the requests but does no longer forwards the requests. Like proxy server, a redirect server makes use of a database or area provider to look up a person. The area statistics, but, is sent back to the caller in a redirection elegance response (3xx), which, after the ACK, concludes the transaction.

Internet Protocol version four (IPv4) Interview Questions
Question 34. Is The Ack Sent To Non-2xx Final Response Is Considered To Be Part Of The Same Transaction As Invite?

Answer :

Yes, the ACK sent to non-2xx final reaction is considered to be part of the same transaction as INVITE. ACK request reuses the equal branch ID as INVITE. Only an ACK despatched in response to a two hundred OK is considered a separate transaction with a completely unique branch ID. Also an ACK to a non-2xx final reaction is a hop-by way of-hop response, not an stop-to-give up reaction.

Question 35. Explain About The Registration Server?

Answer :

A registration server, also known as a registrar, accepts SIP REGISTER requests and all different requests receive a 501 Not Implemented response. The touch statistics from the request is then made to be had to other SIP servers within the identical administrative domain, inclusive of proxies and redirect servers. In a registration request, the To header area carries the name of the aid being registered, and the Contact header fields incorporate the opportunity addresses or aliases. The registration server creates a brief binding between the Address of Record (AOR) URI in the To and the tool URI within the Contact header.

Question 36. Is The Cancel Method Is End-to-give up Request?

Answer :

No, the CANCEL method is hop-via-hop request used to terminate pending calls or searches. A proxy receiving a CANCEL straight away sends a 2 hundred OK response lower back to the sender and generates a brand new CANCEL, that is then forwarded to the next hop. Similar behaviour may be located in 3xx, 4xx, 5xx, and 6xx responses to an INVITE request. While an ACK to a 2xx reaction is generated by the end point, a 3xx, 4xx, 5xx, or 6xx reaction is acknowledged on a hop-with the aid of-hop foundation. A proxy server receiving such a responses right now generates an ACK back to the sender and forwards the response to the following hop.

Spanning Tree Protocol (STP) Interview Questions
Question 37. What Is Sip User Agent?

Answer :

A SIP-enabled give up-tool is called a SIP consumer agent. As the call implies, a consumer agent takes direction or input from a consumer and acts as an agent on their behalf to set up and tear down media periods with different user retailers. In most instances, the person could be a human, but the user could be some other protocol, as within the case of a gateway. A consumer agent need to be capable of establishing a media session with another person agent. A UA must maintain country on calls that it initiates or participates in. A minimum name nation set consists of the local and remote tags, Call-ID, neighborhood and far off CSeq header fields, together with the path set and any state facts essential for the media.

Question 38. What Is The Difference Between Re-invite And Retransmitted Invite?

Answer :

A re-INVITE is used to exchange the session parameters of an present or pending call. It uses the equal Call-ID, however the CSeq is incremented because it's miles a new request. A retransmitted INVITE will comprise the equal Call-ID and CSeq as a preceding INVITE.

Question 39. What Is The Response Send By Ua For Unknown Dialog?

Answer :

A consumer agent receiving a request for an unknown conversation responds with a 481 Dialog/Transaction Does Not Exist. Responses from an unknown dialog are silently discarded.

Question forty. When The Tcp Transport Is Used By Ua?

Answer :

A SIP UA makes use of TCP if it has to ship messages greater than 1,000 octets in length.

Border Gateway Protocol (BGP) Interview Questions
Question 41. What Is Presence Agent?

Answer :

A presence agent (PA) is a SIP tool this is able to receiving subscription requests and producing country notifications. A presence agent can gather presence data from some of gadgets. Presence facts can come from a SIP device registering, a SIP tool publishing presence information  or from many different non-SIP resources.

Question 42. What Is Back-to-again User Agent?

Answer :

A back-to-back person agent (B2BUA) is a sort of SIP tool that receives a SIP request, then reformulates the request and sends it out as a new request. Responses to the request also are reformulated and despatched returned in the contrary path. For example, a B2BUA device can be used to put into effect an anonymizer service in which  SIP UAs can communicate with out either celebration getting to know the alternative birthday party’s URI, IP address, or another statistics. The maximum common form of B2BUA present in SIP networks is software layer gateways (ALG).

Enhanced Interior Gateway Routing Protocol (EIGRP) Interview Questions
Question forty three. What Is Sip Gateway?

Answer :

A SIP gateway is an application that interfaces a SIP network to a community utilizing some other signaling protocol.

Question 44. What Is The Difference Between Media Gateway And Media Gateway Controller?

Answer :

Gateways are sometimes decomposed into a media gateway (MG) and a media gateway controller (MGC). An MGC is occasionally referred to as a call agent because it manages name manipulate protocols (signaling), even as the MG manages the media connection.

Question 45. What Is The Difference Between User Agent And A Gateway?

Answer :

a gateway is just a unique form of person agent, in which the user agent acts on behalf of some other protocol instead of a human. A gateway terminates the signaling direction and can also terminate the media route. Another distinction between a person agent and a gateway is the variety of users supported. While a consumer agent normally supports a unmarried person, a gateway can aid loads or heaps of customers.

Question forty six. Is The Invite Message Will Be Retrasmitted After Recieving 1xx Response?

Answer :

After receiving a 1xx response, any retransmissions quit altogether, and the patron waits for further responses.

Question 47. Can You Explain The Structure Of Sip Protocol?

Answer :

The SIP protocol is split into layers. 
The lowest layer of SIP is its syntax and encoding, wherein the message is constructed. 
The The 2d layer is the delivery layer, it defines how a message is ship and get hold of over a network.
The 0.33 layer is the transaction layer. A transaction is a request sent from the UAC to UAS and the responses for this request coming from UAS to UAC.The transaction layer handles utility-layer retransmissions, matching of responses to requests, and application-layer timeouts.
The layer above the transaction layer is referred to as the transaction person(TU).  Each of the SIP entities, except the stateless proxy, is a transaction consumer.
Question forty eight. What Is Call Statefull Proxy?

Answer :

A proxy is call stateful if it keeps state for a dialog from the beginning INVITE to the terminating BYE request.  A name stateful proxy is constantly transaction stateful, but the communicate is not always actual.

Question 49. What Is Location Service?

Answer :

A vicinity provider is used by a SIP redirect or proxy server to acquire statistics about a callee's possible vicinity(s).  It carries a list of bindings of cope with-of-record keys to 0 or greater touch addresses.

Question 50. What Is Loop?

Answer :

A request that arrives at a proxy, is forwarded, and later arrives lower back at the same proxy.  When it arrives the second time, its Request-URI is identical to the primary time, and different header fields that have an effect on proxy operation are unchanged, so that the proxy would make the same processing selection on the request it made the primary time.  Looped requests are errors and may be handled using the fee of Max-Forwards header discipline.

Question fifty one. What Is Spiral?

Answer :

A spiral is a SIP request that is routed to a proxy, forwarded onwards, and arrives once more at that proxy, however this time differs in a way with the intention to bring about a unique processing selection than the unique request.  Typically, because of this the request's Request-URI differs from its preceding         arrival.  A spiral is not an blunders situation, in contrast to a loop.  A traditional cause for that is call forwarding.  A person calls joe@example.Com.  The instance.Com proxy forwards it to Joe's PC, which in turn, forwards it to bob@example.Com.  This request is proxied returned to the example.Com proxy.  However, this isn't always a loop.  Since the request is focused at a exceptional person, it's far taken into consideration a spiral, and is a valid condition.

Question 52. What Is Loose Routing?

Answer :

A proxy is stated to be loose routing if it follows the procedures described in rfc 3261 specification for processing of the Route header area.  These techniques separate the vacation spot of the request (gift inside the Request-URI) from the set of proxies that need to be visited alongside the manner (present in the Route header subject). A proxy compliant to these mechanisms is likewise called a free router.

Question fifty three. How Do You Avoid The Firewall Issues In Sip Signaling Path?

Answer :

A firewall or a proxy that controls the firewall needs to understand SIP, be capable of parse an INVITE request and 2 hundred OK response, extract the IP addresses and port numbers from the SDP, and open up “pin holes” in the firewall to permit RTP traffic to skip. The hollow can then be closed when a BYE is sent or a session timer expires. An opportunity is an ALG—a B2BUA this is depended on by using the firewall. The firewall then lets in SIP and RTP traffic, which terminates at the ALG and blocks all different visitors. The authentication and protection regulations of permitting or denying SIP periods are then managed with the aid of the SIP ALG in preference to within the firewall itself.

Question fifty four. What Is Stun Protocol?

Answer :

The Simple Traversal of UDP through NATs (STUN) protocol  lets in a client to discover the presence and kind of NATs among the purchaser and the general public Internet. In addition, a customer can discover the mapping among the private IP cope with and port variety and the general public IP cope with and port range. Typically, a carrier issuer will function a STUN server within the public Internet, with STUN customers being embedded in end-devices, which are probably in the back of a NAT.

Question 55. What Is Turn Protocol?

Answer :

Traversal Using Relay NAT (TURN) protocol allows a customer to gain a delivery IP cope with and port that it can receive packets despatched from a single IP address inside the public Internet. For a few NAT topologies which includes a customer behind a symmetric NAT, using a relay placed inside the public Internet is the best method that permits verbal exchange to take region.

Question fifty six. Can You List Out The Sip Methods?

Answer :

The INVITE, REGISTER, BYE, ACK, CANCEL, and OPTIONS techniques are the authentic six techniques in SIP. The REFER, SUBSCRIBE, NOTIFY,MESSAGE, UPDATE, INFO, and PRACK techniques are defined in separate RFCs.

Question fifty seven. If The Re-invite Is Failed Or Refused, Will The Call/session Discontinued?

Answer :

No, If a re-INVITE is refused or fails in any way, the consultation maintains as though the INVITE had in no way been despatched.

Question fifty eight. What Is The Significance Of The Expires Header In An Invite Message?

Answer :

An Expires header in an INVITE shows to the USAhow long the call request is legitimate. For example, the U.S.Could depart an unanswered INVITE request displayed on a display screen all through certain inside the Expires header. Once a session is mounted, the Expires header has no meaning—the expiration of the time does no longer terminate the media session. Instead, a Session-Expires header can be used to location a time restriction on a longtime session.

Question 59. What Is The Significance Of Invite Message?

Answer :

The INVITE technique is used to set up media periods among person sellers. An INVITE normally has a message frame containing the media records of the caller. If an INVITE does not contain media statistics, the ACK carries the media facts of the UAC. If the media facts contained within the ACK isn't acceptable, then the called party must ship a BYE to cancel the consultation—a CANCEL can't be sent due to the fact the consultation is already set up.

Question 60. What Is The Significance Of The Register Message?

Answer :

The REGISTER approach is utilized by a user agent to notify a SIP network of its cutting-edge Contact URI (IP deal with).

Question 61. What Is The Registration And Why It Is Required?

Answer :

The registration creates a transient binding between the Address of Record (AOR) URI inside the To header and the tool URI within the Contact header.The binding of  Registration is not required to enable a user agent to apply a proxy server for outgoing calls. It is important, however, for a person agent to sign in to receive incoming calls from proxies that serve that area until a few non-SIP mechanism is used by the region service to populate the SIP URIs and Contacts of quit-factors.

Question 62. What Is The Significance Of The Expires Header In Register Message?

Answer :

The presence of an Expires header sets the expiration of Contacts and not using a expires parameter. If an expires parameter is present, it sets the expiration time for that Contact best.

Question sixty three. What Is The Significance Of The Request-uri In Register Message?

Answer :

The Request-URI incorporates most effective the domain of the registrar server without a person element.

Question sixty four. What Is Third Party Registration?

Answer :

If the UA sending the registration request on behalf of other UA it's miles known as 0.33 birthday celebration registration. In this case, the From header will comprise the URI of the birthday celebration submitting the registration on behalf of the birthday celebration recognized in the To header.

Question sixty five. How To Cancel All The Registrations Using A Single Register Message?

Answer :

The contact header subject is same to * and Expires: 0

Question sixty six. How Do You Retrive All The Registered Contacts Using A Single Register Message?

Answer :

If no Contact header found in REGISTER message registrar/region server will go back all modern-day registrations(contacts) in reaction.

Question sixty seven. What Is The Significance Of Bye Message?

Answer :

The BYE technique is used to terminate an established media consultation. A BYE is despatched simplest through person marketers collaborating in the consultation, in no way with the aid of proxies or different 1/3 parties. It is an stop-to-quit method, so responses are only generated by way of the other person agent.

Question 68. What Is The Significance Of Ack Message?

Answer :

The ACK method is used to well known final responses to INVITE requests. Final responses to all other requests are never stated.An ACK might also incorporate an software/sdp message body. This is allowed if the initial INVITE did no longer contain a SDP message body. If the INVITE contained a message body, the ACK won't contain a message body. For 2xx responses, the ACK is end-to-give up, however for all other very last responses it's far performed on a hop-by way of-hop basis when stateful proxies are concerned. A hop-through-hop ACK reuses the identical department ID because the INVITE considering it is considered a part of the equal transaction. An end-to-quit ACK uses a one of a kind department ID as it's miles taken into consideration a new transaction.

Question sixty nine. What Is The Significance Of Cancel Method?

Answer :

The CANCEL approach is used to terminate pending searches or call attempts. It may be generated with the aid of both consumer marketers or proxy servers supplied that a 1xx reaction containing a tag has been received, however no very last reaction has been acquired. The branch ID for a CANCEL fits the INVITE that it's miles canceling. A CANCEL best has which means for an INVITE since most effective an INVITE might also take numerous seconds (or mins) to complete. All other SIP requests entire immediately. A consumer agent confirms the cancellation with a 2 hundred OK reaction to the CANCEL and replies to the INVITE with a 487 Request Terminated response.

Question 70. What Is The Significance Of Options Method?

Answer :

The OPTIONS technique is used to question a consumer agent or server about its abilities and find out its present day availability.

Question seventy one. What Is The Significance Of Refer Method?

Answer :

The REFER method is utilized by a user agent to request some other person agent to get right of entry to a URI or URL resource. The aid is recognized by means of a URI or URL inside the required Refer-To header subject. A REFER request can be despatched either internal or out of doors an present dialog.

Question seventy two. What Is The Significance Of Subscribe Method?

Answer :

The SUBSCRIBE approach is utilized by a user agent to establish a subscription for the purpose of receiving notifications (via the NOTIFY technique) about a particular event. A a success subscription establishes a dialog between the UAC and the UAS. The subscription request carries an Expires header field, which suggests the desired duration of the existence of the subscription. After this term passes, the subscription is mechanically terminated. The subscription may be refreshed via sending another SUBSCRIBE inside the dialog before the expiration time. A server accepting a subscription returns a two hundred OK reaction additionally containing an Expires header area. The expiration timer may be the same as the request, or the server may additionally shorten the c language, however it is able to no longer prolong the c program languageperiod. There is not any "UNSUBSCRIBE" technique utilized in SIP—rather a SUBSCRIBE with Expires:0 requests the termination of a subscription and subsequently the conversation. A terminated subscription (both because of timeout out or a termination request) will bring about a final NOTIFY indicating that the subscription has been terminated.

Question seventy three. What Is The Significance Of Notify Method?

Answer :

The NOTIFY technique is used by a person agent to deliver facts about the occurrence of a particular occasion. A NOTIFY is constantly sent inside a dialog while a subscription exists among the subscriber and the notifier. A NOTIFY request generally gets a 200 OK response to indicate that it has been obtained. If a 481 Dialog/Transaction Does Not Exist reaction is obtained, the subscription is automatically terminated and no more NOTIFYs are despatched. NOTIFY requests incorporate an Event header area indicating the package deal and a Subscription-State header subject indicating the contemporary nation of the subscription.

Question 74. What Is The Significance Of Message Method?

Answer :

The MESSAGE method is used to transport instantaneous messages (IM) using SIP. IM typically includes brief message exchanged in close to-real time by way of participants engaged in a "communication." MESSAGEs may be sent inside a conversation or out of doors a conversation, but they do no longer establish a dialog by themselves.

Question seventy five. What Is The Significance Of Info Method?

Answer :

The INFO technique is used by a consumer agent to ship name signaling facts to another consumer agent with which it has a longtime media session. This isn't like a re-INVITE because it does not trade the media characteristics of the decision. The request is end-to-stop, and is never initiated by means of proxies. A proxy will constantly forward an INFO request—it is as much as the U.S.To check to see if the dialog is legitimate. INFO requests for unknown dialogs get hold of a 481 Transaction/Dialog Does Not Exist reaction.

Question 76. What Is The Significance Of Prack Method?

Answer :

The PRACK approach is used to acknowledge receipt of reliably transported provisional responses (1xx). The reliability of 2xx, 3xx, 4xx, 5xx, and 6xx responses to INVITEs is completed the usage of the ACK approach. However, in instances wherein a provisional response, together with one hundred eighty Ringing, is critical in determining the call country, it may be necessary for the receipt of a provisional response to be showed. The PRACK approach applies to all provisional responses besides the a hundred Trying reaction, that's never reliably transported. A PRACK is generated with the aid of a UAC whilst a provisional response has been acquired containing a RSeq dependable sequence quantity and a Supported: 100rel header. The PRACK reproduction the number inside the RSeq and the CSeq of the reaction in a RAck header.

Question seventy seven. What Is The Significance Of Update Method?

Answer :

The UPDATE method is used to adjust the nation of a session without converting the country of the conversation. A consultation is hooked up in SIP the usage of an INVITE request in a proposal/answer way. Typically, a session provide is made in the INVITE and a solution made in a reaction to the INVITE. In a longtime consultation, a re-INVITE is used to update session parameters. However in pending consultation (INVITE sent however no very last reaction obtained) UPDATE is used to update consultation parameters. Basically UPDATE is used to perform QoS and negotiate give up-to-give up attributes previous to consultation status quo.